No Risk for HIV Transmission in Serodiscordant Gay Couples When Viral Suppression Is Achieved

There is zero risk for HIV transmission in serodiscordant gay couples through condomless sex when the partner with HIV is receiving suppressive ART.

There is zero risk for HIV transmission in serodiscordant gay couples through condomless sex when the partner with HIV is receiving suppressive antiretroviral therapy (ART), according to a study published in the Lancet.

Similar to the first phase of the PARTNER study, which showed no HIV transmission in serodiscordant heterosexual couples, the primary aim of this second phase of the PARTNER study was to produce a similar level of evidence for transmission risk through condomless anal sex between serodiscordant gay men with suppressive ART.

In this prospective, observational study, researchers recruited 782 serodiscordant gay couples from 75 sites in 14 European countries. Data were collected at baseline and then every 4 to 6 months during study visits, which included sexual behavior questionnaires, HIV testing for the partner without HIV, and HIV-1 viral load testing for the partner with HIV. If HIV transmission occurred between the serodiscordant couple, anonymized phylogenetic analysis of HIV-1 pol and env sequences were compared in both partners to identify linked transmission.

Incidence rate of HIV transmission was calculated as the number of phylogenetically linked HIV infections that occurred during eligible couple-years of follow-up divided by the number of eligible couple-years of follow-up. Couple-years of follow-up were eligible for inclusion if condomless sex was reported, use of preexposure prophylaxis or postexposure prophylaxis was not reported by the partner without HIV, and the partner with HIV was virally suppressed (defined as plasma HIV-1 RNA <200 copies/mL) at the most recent visit and within the last 12 months.

Participants provided 1593 couple-years of follow-up, with a median follow-up of 2 years. Median age was 38 years in participants without HIV and 40 years in partners with HIV, and couples reported having condomless sex with their partners for a median of 1 year.

In total, couples reported having condomless anal sex approximately 76,088 times during eligible couple-years of follow-up. The median number of times couples had condomless sex was 43 times per year. There were 288 (37%) of 777 partners without HIV who reported condomless sex with other partners. Although 15 of the participants who initially did not have HIV became HIV-1 positive during eligible couple-years of follow-up, none were within-couple phylogenetically linked transmissions, resulting in an HIV transmission rate of zero, with an upper 95% CI of 0.23 per 100 couple-years of follow-up, equivalent to 1 transmission per 435 years of condomless sex.

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A quarter of participants both with and without HIV reported having a sexually transmitted infection during follow-up, and although there were fewer couple-years of follow-up during these periods (116 couple-years of follow-up), no linked transmissions occurred. In addition, 19.3 couple-years of follow-up were not eligible for inclusion in the primary analysis because the HIV viral load of the partner with HIV was >200 copies/mL for at least 1 day, but all other criteria for eligibility were met. During this time, no phylogenetically linked transmissions occurred, despite couples having sex 810 times without condoms.

“Our findings support the message of the U=U (undetectable equals untransmittable) campaign,” concluded the researchers. Although the U=U campaign can be hard to apply when people with HIV do not have access to testing, effective treatment, viral load monitoring, and support to reach and maintain viral suppression, the dissemination of this campaign is “necessary to promote the benefits of early testing and treatment and to tackle stigma, discrimination, and criminalization laws that continue to affect HIV-positive people.”


Rodger AJ, Cambiano V, Bruun T, et al; PARTNER Study Group. Risk of HIV transmission through condomless sex in serodifferent gay couples with the HIV-positive partner taking suppressive antiretroviral therapy (PARTNER): final results of a multicentre, prospective, observational study [published online May 2, 2019]. Lancet. doi:10.1016/S0140-6736(19)30418-0